void QueueInit(Que* pq)
{
    assert(pq);

    pq->head = pq->tail = NULL;
    pq->size = 0;
}

void QueueDestroy(Que* pq)
{
    assert(pq);

    QNode* cur = pq->head;
    while (cur)
    {
        QNode* next = cur->next;
        free(cur);
        cur = next;
    }

    pq->head = pq->tail = NULL;
    pq->size = 0;
}

void QueuePush(Que* pq, QDataType x)
{
    assert(pq);

    QNode* newnode = (QNode*)malloc(sizeof(QNode));
    if (newnode == NULL)
    {
        perror("malloc fail");
        exit(-1);
    }

    newnode->data = x;
    newnode->next = NULL;

    if (pq->tail == NULL)
    {
        pq->head = pq->tail = newnode;
    }
    else
    {
        pq->tail->next = newnode;
        pq->tail = newnode;
    }

    pq->size++;
}

void QueuePop(Que* pq)
{
    assert(pq);
    assert(!QueueEmpty(pq));

    if (pq->head->next == NULL)
    {
        free(pq->head);
        pq->head = pq->tail = NULL;
    }
    else
    {
        QNode* next = pq->head->next;
        free(pq->head);
        pq->head = next;
    }

    pq->size--;
}

QDataType QueueFront(Que* pq)
{
    assert(pq);
    assert(!QueueEmpty(pq));

    return pq->head->data;
}

QDataType QueueBack(Que* pq)
{
    assert(pq);
    assert(!QueueEmpty(pq));

    return pq->tail->data;
}

bool QueueEmpty(Que* pq)
{
    assert(pq);

    return pq->head == NULL;
}

int QueueSize(Que* pq)
{
    assert(pq);

    return pq->size;
}